Lasers are used as light sources in many consumer and industrial products including laser printers and optical communication links. In laser printers, light output of the laser may be modulated to selectively discharge the photoconductive drum. In optical communication links, the light output of the laser may be modulated to represent the states of a digital information signal. Lasers having a modulated light output are also used to write a digital information signal on an optical disc, for example. In these and other applications, the need to modulate the output of the laser to controlled power levels normally precludes modulating the light output by simply switching the laser on and off.
Recently, vertical-cavity surface-emitting lasers (VCSELs) have been introduced. Such lasers may be formed in a structure of semiconductor layers deposited on a semiconductor substrate, and emit light from a port in the surface of the structure, instead of from a very narrow region on the cleaved edge of the device, as in an edge-emitting laser. A VCSEL offers numerous performance advantages over an edge-emitting laser. For example, a VCSEL inherently has a smaller numeric aperture and generates a light beam of increased symmetry compared with an edge-emitting laser. As a result, the light from the VCSEL can be coupled into an optical system of the laser printer or optical communication link more efficiently than the light from the edge-emitting laser. However, the VCSEL generally emits a light beam in a single direction instead of the multiple light beams emitted by the edge-emitting laser. Accordingly, a VCSEL-based light source generating light with a controlled intensity cannot be implemented simply by substituting a VCSEL for an edge-emitting laser in a laser scanning apparatus which utilizes a second light beam from the source for controlling the output of the source. An alternative arrangement is desired to monitor and/or control the intensity of the light generated by the VCSEL.
Some devices split off a portion of a light beam output from a VCSEL light source and direct one of the beams towards a monitor photodiode. However, splitting of the light beam for monitoring involves additional complexity along with added costs.
Aspects described herein provide improved laser scanning apparatuses and laser scanning methods.